Activated alumina is prepared by thermal dehydration (300°-600°C) of chemically pure aluminium hydroxide. The prepared materials have been characterized by residual water content, BET surface area and hydraulic activity. These aluminas are incorporated in cement free castable batch. Important properties like bulk density, apparent porosity, linear change, cold compressive strength, strength retainment after thermal shock have been studied. X-ray diffraction analysis has been performed to identify the phases formed while SEM studies have been used to get an idea about the microstructure of the castable matrix. © 2009 Taylor and Francis Group, LLC.